Postfix

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Revision as of 01:25, 21 July 2013 by Abrambleninja(talk | contribs)(The `courier-imap' package was apparently dropped from the official packages as well as squirrelmail, so I added that to the info pane.)

"Postfix attempts to be fast, easy to administer, and secure, while at the same time being sendmail compatible enough to not upset existing users. Thus, the outside has a sendmail-ish flavor, but the inside is completely different."

The goal of this article is to setup Postfix for virtual mailbox delivery only. There will be no delivery to user accounts on the system (/etc/passwd). Further, access will only be available via a web mail frontend (Squirrelmail), no direct POP3 or IMAP access will be granted. It should be fairly easy to allow those additional features given the information below, but it is not within the scope of this document.

Required packages

The factual accuracy of this article or section is disputed.

Reason: The squirrelmail and courier-imap packages have been dropped from the offical repositories and moved to the AUR. roundcubemail is an officially supported possible alternative to Squirrelmail (Discuss in Talk:Postfix#)

Postfix configuration

Step 1: check /etc/passwd, /etc/group

After Postfix installation, make sure that the following shows up in /etc/passwd:

postfix:x:73:73::/var/spool/postfix:/bin/false

Make sure that the following shows up in /etc/group:

postdrop:x:75:
postfix:x:73:

Note: Postfix can be made to run in a chroot. This document does not currently cover this and might be added later.

Step 2: setup MX record

An MX record should point to the mail host. Usually this is done from configuration interface of your domain provider.

A mail exchanger record (MX record) is a type of resource record in the Domain Name System that specifies a mail server responsible for accepting email messages on behalf of a recipient's domain.

When an e-mail message is sent through the Internet, the sending mail transfer agent queries the Domain Name System for MX records of each recipient's domain name. This query returns a list of host names of mail exchange servers accepting incoming mail for that domain and their preferences. The sending agent then attempts to establish an SMTP connection to one of these servers, starting with the one with the smallest preference number, delivering the message to the first server with which a connection can be made.

Note: Some mail servers will not deliver mail to you if your MX record points to a CNAME. For best results, always point an MX record to an A record definition. For more information, see e.g. Wikipedia's List of DNS Record Types.

Step 3: /etc/postfix/master.cf

This is the Pipeline configuration file, in which you can put your new pipes e.g. to check for Spam!

Step 4: /etc/postfix/main.cf

For virtual mail

Step 4.1 myhostname

set myhostname if your mail server has multiple domains, and you do not want the primary domain to be the mail host. The default is to use the result of a gethostname() call if nothing is specified.
For our purposes we will just set it as follows:

myhostname = mail.nospam.net

This is assuming that a DNS A record, and an MX record both point to mail.nospam.net

Step 4.2 mydomain

this is usually the value of myhostname, minus the first part. If your domain is wonky, then just set it manually:

mydomain = nospam.net

Step 4.3 myorigin

this is where the email will be seen as being sent from. I usually set this to the value of mydomain. For simple servers, this works fine. This is for mail originating from a local account. Since we are not doing local delivery (except sending), then this is not really as important as it normally would be.

myorigin = $mydomain

Step 4.4 mydestination

This is the lookup for local users. Since we are not going to deliver internet mail for any local users, set this to localhost only.

mydestination = localhost

Step 4.5 mynetworks and mynetwork_style

Both of these control relaying, and whom is allowed to. We do not want any relaying.
For our sakes, we will simply set mynetwork_style to host, as we are trying to make a standalone postfix host, that people with use webmail on. No relaying, no other MTA's. Just webmail.

mynetworks_style = host

Step 4.6 relaydomains

This controls the destinations that Postfix will relay TO. The default value is $mydestination. This should be fine for now.

relay_domains = $mydestination

Step 4.7 home_mailbox

This setting controls how mail is stored for the users.
Set this to "Maildir/", as courier IMAP requires Maildir style mail storage. This is a good thing. Maildir format mailboxes remove the possible race conditions that can occur with old style mbox formats. No more need to deal with file locking. The '/' at the end is REQUIRED.

home_mailbox = Maildir/

Step 4.8 virtual_mail

Virtual mail is mail that does not map to a user account (/etc/passwd). This is where all the email for the system will be kept. We are not doing local delivery, remember, so if you want a user that has the same name as a local user, just make a virtual account with the same name.
First thing we need to do is add the following:

virtual_mailbox_domains is a list of the domains that you want to receive mail for. This CANNOT be the same thing that is listed in mydestination. That is why we left mydestination to be localhost only.
virtual_mailbox_maps will contain the info about the virtual users and their mailbox locations. We are using a hash file to store the more permanent maps, and these will override the forwards in the MySQL database.

virtual_mailbox_base is the base dir where the virtual mailboxes will be stored.
The gid and uid maps are the real system user account that the virtual mail will be owned by. This is for storage purposes. Since we will be using a web interface, and do not want people accessing this by any other means, we will be creating this account later with no login access.
Virtual_mailbox_limit controls the size of the mailbox. I do not know how well this works yet. I have set the size above to about 50MB.

Step 4.9 Default message and mailbox size limits

Postfix imposes both message and mailbox size limits by default. The message_size_limit controls the maximum size in bytes of a message, including envelope information. (default 10240000) The mailbox_size_limit controls the maximum size of any local individual mailbox or maildir file. This limits the size of any file that is written to upon local delivery, including files written by external commands (i.e. procmail) that are executed by the local delivery agent. (default is 51200000, set to 0 for no limit) If bounced message notifications are generated, check the size of the local mailbox under /var/spool/mail and use postconf to check these size limits:

If you want to control where the mail gets delivered and which mailbox format is to be used, you can do this by setting:

home_mailbox = /some/path

or:

mail_spool_directory some/path

mail_spool_directory is an absolute path where all mail goes, while home_mailbox specifies a mailbox relative to the user's home directory. If the path ends with a slash ('/'), messages are stored in Maildir format (directory tree, one message per file); if it doesn't, the mbox format is used (all mail in one file).

Examples:

mail_spool_directory = /var/mail (1)
home_mailbox = Maildir/ (2)

1) All mail will be stored in /var/mail, mbox format.

2) Mail will be saved in ~/Maildir, Maildir format.

Step 4: /etc/postfix/aliases

We need to map some aliases to real accounts. The default setup by arch looks pretty good here.

Uncomment the following line, and change it to a real account. I put the user account on the box that I use. Best not to just send mail to root, because you do not want to be logging in as root or checking email as root. Not good. Sudo is your friend, and so is forwarding root mail. Since this is for local delivery only (syslogs and stuff), it is still within the realm of mydestination.

root: USER

Once you have finished editing /etc/postfix/aliases you must run the postalias command:

Instead of having a directory structure something like /home/vmail/example.com/user@example.com you can have cleaner subdirectories (without the additional domain name) by replacing select_field and where_field with:

The key is the last entry. This is an actual email, if you see that, it is working.

Configure Courier IMAP

Step 1: /etc/courier-imap/imapd

ADDRESS=127.0.0.1

We set the listen address to LOCAL ONLY. No outside connections.

Step 2: /etc/authlib/authdaemonrc

Remove all the modules from the authmodulelist line except for authmysql like so:

authmodulelist="authmysql"

Step 3: /etc/authlib/authmysqlrc

Replace the entire file with the following:

MYSQL_SERVER localhost
MYSQL_USERNAME postfixuser
MYSQL_PASSWORD secret
MYSQL_SOCKET /run/mysqld/mysqld.sock
MYSQL_DATABASE postfix
# MYSQL_NAME_FIELD name
MYSQL_USER_TABLE users
MYSQL_CLEAR_PWFIELD password
MYSQL_UID_FIELD '5003'
##note, this is the uid that we set in /etc/postfix/main.cf
MYSQL_GID_FIELD '5003'
##note, this is the gid that we set in /etc/postfix/main.cf
MYSQL_LOGIN_FIELD email
MYSQL_HOME_FIELD "/home/vmailer"
MYSQL_MAILDIR_FIELD concat(domain,'/',email,'/')
MYSQL_QUOTA_FIELD quota

Where secret is the MySQL password for the user postfixuser.
If you are using encrypted passwords by using MySQL's encrypt function. Use "MYSQL_CRYPT_PWFIELD columnname" instead of "MYSQL_CLEAR_PWFIELD columnname".

For an alternative directory structure, you could also use this setting for MAILDIR_FIELD:

Step 1.3: Generate a certificate

Step 1.4: restart Apache and test

Make sure that https is now working, and that you can get to the secure site.

Step 2: put Squirrelmail in the directory you created

Either extract squirrelmail, or move it from where the arch package puts it, into the directory you created for the secure http site.

Step 3: run Squirrelmail config utility

cd squirrelmaildir/config
perl conf.pl

Make sure you select 'D', then type in courier and hit enter. Make sure your other options are correct as well.
Note: If you use php with safe mode on, make sure that the data dir is owned by the same owner as all the files in the squirrelmail directory. With safe mode off, simply follow the squirrelmail setup directions.

Step 4: test the Squirrelmail setup

Point your browser to squirrelmail/src/configtest.php. Should you get an error on directory location, make sure php.ini has been set to allow access to them (open_basedir directive).

Step 5: test Squirrelmail

Log in with the test account. You will need to login with the form of:
username: cactus@virtualdomain.tld
password: secret

Try sending email to non-existent local accounts. You should get an immediate bounce back.
Try sending email to external good email accounts, as well as non-existent ones.
Just general testing stuff.
If everything works fine, then you can add other accounts to the MySQL database, and away you go!

Troubleshooting

If you received an error similar to:

Warning: file_exists() [function.file-exists]: open_basedir restriction in effect. File(/var/lib/squirrelmail/data) is not within the allowed path(s): \
(/srv/http/:/home/:/tmp/:/usr/share/pear/) in /home/httpd/site.virtual/virtualdomain.tld/html/squirrelmail/src/configtest.php on line 303